The present invention relates to a permanent-magnet motor and its manufacturing method used for such as an air conditioner and a compressor for a refrigerator.
FIG. 9 shows a conventional permanent-magnet motor.
In FIG. 9, a stator 1 consists of a circular stator core 2, plural teeth 3 provided to the stator core 2, and coils 4 wound around the teeth 3. The stator 1 is, for example, a distributed winding stator having stator winding of plural phases.
Inside of the stator 1, a rotor 10 is placed rotatably with a gap 5. The rotor 10 has a rotation axis 11 and a rotor core 12 provided around the rotation axis 11.
As shown in the figure, the permanent-magnet motor, in which a permanent magnet is used for a rotor of the motor, is formed by inserting plural permanent magnets 14, each of which has an arc in the view of its cross section, into a rotor core 12 having plural containing holes 13 provided near the peripheral part for inserting the plural permanent magnets. Each permanent magnet 14 is placed so that the convex part should face to an outside.
Each permanent magnet 14 is magnetized so that magnetic orientation 15 of each piece should be parallel with a direct line connecting the center of the rotor 10 and the center part of the circumference of the permanent magnet 14, namely, the center of the magnetic orientation should be infinite. The rotor core 12 is made by multilayering multiple silicon steel plates respectively having the containing holes 13.
However, as for the permanent-magnet motor structured according to the first related art, the distribution of the magnetic flux density of the gap between the rotor 10 and the stator 1, generated by the permanent magnet 14, is in a wave form as shown in FIG. 11. Since this wave form is much different from sine wave, a problem is raised such as large cogging torque and much vibration and noise.
To solve the above problem, another technique has been developed as shown in FIG. 12. The rotor 10 of the figure is magnetized so that the focus of the magnetic orientation 15 of each piece of the permanent magnet 14 should be located outside of the rotor 10.
Using the above means, the magnetic flux density of the gap becomes high at the center part of the magnetic pole, while the density becomes low at both ends of the magnetic pole. Consequently, the distribution of the magnetic flux density of the gap resembles to the sine wave, which enables to decrease the cogging torque and also reduce the vibration and the noise.
However, in the motor structured as described above, the magnetic orientation 15 should be focused to the convex part of the permanent magnet 14 on producing the permanent magnet 14. That is, the center of the magnetic orientation is placed in the opposite direction to the center of the arc formed due to the shape of the permanent magnet itself, which causes to differentiate the direction of the magnetic flux from the direction of compression at manufacturing process of the permanent magnet. Consequently, the residual magnet flux density becomes low, accompanied by reducing the efficiency of the motor.
Another means to solve the problem raised in the above first related art can be considered as a structure shown in FIG. 14. In this rotor 10, the convex part of each piece of the permanent magnet 14 is placed so as to face the inside of the rotor core 12, and each piece of the permanent magnet is magnetized so that the focus of the magnetic orientation of each piece of the permanent magnet 14 is located outside of the rotor 10.
Employing the above means, the distribution of the magnetic flux density of the gap is high at the center part of the magnetic pole and low at the both ends. That is, the distribution becomes close to the sine wave as shown in FIG. 15. Accordingly, the cogging torque can be decreased, the vibration and the noise can be reduced. On manufacturing the permanent magnet 14, the magnetic orientation 15 can be focused at the concave part of the permanent magnet 14. Namely, the center of the magnetic orientation becomes in the same direction to the center of the arc formed due to the shape of the permanent magnet itself, and therefore, the direction of compression at producing the permanent magnet also becomes the same to the direction of the magnetic flux. The residual magnetic flux density is not lowered nor the efficiency of the motor becomes worse.
However, in the structure of the rotor according to the third related art explained above, the thickness of-a rotor core part 12a which separates the gap 5 and each of the permanent magnet 14 becomes increased, and the magnetic resistance becomes low. Consequently, among magnetic flux 20 generated by electric current of the coil 4, the amount of the magnetic flux which passes through the rotor core part 12a and short-circuits with the teeth 3 of the stator core 2 becomes large. Accordingly, the torque ripple generated by the fundamental wave component and higher harmonic wave component also becomes increased, which causes to enlarge the vibration and the noise.
The present invention aims to provide, for example, a permanent-magnet motor, having a permanent magnet, which can reduce the vibration and the noise without decreasing the efficiency of the motor and a manufacturing method for the permanent-magnet motor.
According to the preferred embodiment of the present invention, a permanent-magnet motor and a manufacturing method for the permanent-magnet having:
a stator having stator winding of plural phases; and
a rotor facing to inside of the stator across a gap part, and having a rotor core and a permanent magnet-provided to the rotor core,
wherein the permanent magnet is made so as to have both of a convex part to an inner diameter side and a convex part to an outer diameter side in a cross section taken vertically to an axis; and
wherein a focus of magnetic orientation of each magnetic pole of the permanent-magnet is located outside of the rotor.
Further, the rotor is formed by a rotor core assembly made by multilayering multiple pieces of core laminations, each having plural containing holes for inserting the permanent magnets, and the permanent magnets are inserted into the containing holes for inserting the permanent magnets and a thickness of the rotor core, which separates the permanent magnet and the gap, is made within xc2x130% of a thickness of the rotor core lamination.
Further, the rotor is formed by including the permanent magnets in an outer peripheral part of the rotor core and a non-magnetic protect pipe is attached around the permanent magnets.
Further, when a radius of an arc of an outer diameter side of the containing hole provided to the rotor core for inserting the permanent magnet is R, and a radius of an arc of an outer diameter side of the permanent magnet inserted into the containing hole is r, it is set as R less than r.
Further, in the permanent-magnet motor, in which a thickness of the rotor core separating the permanent magnet and the gap part is made within xc2x130% of a thickness of the multiple rotor core laminations, the stator is a concentrated winding stator made by directly winding a coil around a teeth part of the stator.
Further, a radius of the convex part to the inner diameter side of the permanent magnet is smaller than a radius of the convex part to the outer diameter side of the permanent magnet.
Yet further, a straight line part is provided to each of a part of an arc of an inner diameter side of the containing hole for inserting the permanent magnet and a part of an arc of an inner diameter side of the permanent magnet.